Military bomb

ABSTRACT

A military bomb is provided which has an elastomeric tail pad and seal formed from a composition including the reaction product of a mixture of asphaltic filler; hydroxy terminated polydiene; non-volatile organic polyisocyanate.

United States Patent Dereich et a1.

[4 1 Sept. 26, 1972 MILITARY BOMB Inventors: John E. Dereieh, Edgeworth; James E. Gleeson; Glenn .1. Earle, both of Pittsburgh, all of Pa.

Assignee: H. H. Robertson Company, Pittsburgh, Pa.

Filed: Nov. 2, 1970 Appl. No.: 86,089

US. Cl. ..102/2, 86/1 R Int. Cl ..F42b 25/10 Field of Search ..206/41 C; 102/2-4,

[56] References Cited UNITED STATES PATENTS 3,188,962 6/1965 Mosher ..86/1 R X 3,243,956 4/1966 Hamm et al ..86/1 R X 1,316,296 9/1919 Gathmann 102/2 2,733,658 2/1956 Moat 102/24 R 2,890,615 6/1959 Lefebure 102/43 P Primary Examiner-Samuel W. Engle Attorney-George E. Manias and Harry B. Keck [57] ABSTRACT A military bomb is provided which has an elastomeric tail pad and seal formed from a composition including the reaction product of a mixture of aspha1tic filler; hydroxy terminated polydiene; non-volatile organic polyisocyanate.

4 Claims, Drawing Figure PA'TE'N'TEDserzs I972 3.693; 548

INVENTORS. JOHN E. DEREICH BY GLENN J. EARLE JAMES E. GLEESON FT OQN E M MILITARY BOMB BACKGROUND OF THE INVENTION l. Field of the Invention Military bombs. More particularly, an elastomeric tail pad and seal for military bombs and a method of installing the same. I

2. Description of the Prior Art Military bombs at the present time are normally filled with molten explosive compositions while in a vertical disposition with the closed nose pointed downwardly. The bomb casings are maintained in the vertical position for appreciable periods of time until the molten explosive composition congealsThereafter a tail pad and seal is applied to confine the explosive composition with the bomb casing and to insulate the explosive composition from contact with the subsequently installed metal tail plugs. In the past, molten wax and resin mixture has been employed as a tail pad. Also asphaltic compositions have been employed as the tail pad. All of these prior art compositions have exhibited shortcomings. For example, the molten wax cannot be applied until the explosive composition has congealed and cooled. The molten wax and resin mixture and the asphaltic compositions are not effective as seals.

SUMMARY OF THE INVENTION According to the present invention a military bomb tail pad and seal is provided by curing a thermosettable mixture including:

' asphaltic filler material;

polydiene hydroxy terminated polymer;

non-volatile organic polyisocyanate;

suitable catalyst for the reaction of isocyanate groups and hydroxyl groups.

The composition may be filled with inert particulate fillers such as silica, calcium carbonate, ground glass and the like and may include suitable extender oils.

BRIEF DESCRIPTION OFF THE DRAWINGS The single drawing illustrates in cross-section a typical military bomb casing.

DESCRIPTION OF THE PREFERRED EMBODIMENT( S) A typical military bomb includes a metal body or casing 11 having an internal lining 12 consisting of an asphaltic coating or a plastisol. The casing 11 has a nose well 13, plug wells 14, an activator well 15 and a tail opening 16. The wells l3, l4, 15, 16 are provided with threads to receive plugs or closures such as a nose plug 18, and a tail plug 19. A nose fuse20 is connected to the tail plug 19. A nose conduit 22 and a tail conduit 23 connect the nose fuse 20 and the tail fuse 2] respectively to the activator well 15. The interior of the bomb casing 11 is filled with an explosive mass 25, for example, TNT, tritonal, picratol. A resilient tail pad and seal 26 serves as a cap over the mass 25 of explosive material.

The present invention is concerned with improvements in the tail pad and seal 26.

It will be observed that the tail pad and seal 26 communicates with the inner wall of the casing 11 and covers the mass 25 of the explosive composition. The

present improved tail pad consists of the thermoset reaction product of:

asphaltic filler;

hydroxy terminated polydiene polymer;

polyisocyanate;

plasticizer oil. The pad 26 adheres to the inner wall of the bomb casing 11. It may be desirable to include a primer on the inner wall of the bomb casing where the pad 26 is to be adhered. An excellent primer for this purpose is a reactive silicone. The pad 26 may also include inert particulate fillers.

The military bomb tail pad and seal composition is formulated preferably from two storageable components which are identified for convenience as Component A and Component B. Component A includes hydroxy terminated polydiene and a suitable catalyst for the reaction of hydroxyl groups with isocyanate groups, for example, an alkyl tin catalyst. Component B includes a non-volatile organic polyisocyanate. In addition to these described ingredients, the storageable components also include petroleum asphalt and/or plasticizer oil. Preferably some of the asphalt and some of the plasticizer mineral oil is provided in each of the two Components A and B in such proportions that the two components will have approximately equal volume and approximately equal viscosity. Preferably the composition will contain particulate extenders such as calcium carbonate, silica. The two Components A and B are shipped and stored separately until ready for use. Two components are mixed together as a thick fluid which is poured or extruded into the bomb casing after the explosive composition is introduced. The gel time or cure time of the composition may be regulated as desired in the manner hereinafter set forth. Normally the explosive composition is introduced into the bomb casing while the bomb casing is maintained in a vertical position with the nose downwardly. The explosive composition normally is heated to a molten state prior to pouring into the military bomb casing. The present tail pad and seal can be poured on top of the molten explosive composition before or after the composition congeals. Alternatively, the present composition can be applied after the explosive composition has congealed. In the event a particulate explosive composition is employed, the present tail pad composition also has utility, serving to seal off the inventory of explosive particles.

The present tail pad and seal exhibits exceptional adhesive properties in its connection with the interior side walls of the casing 11. The present tail pad and seal, after curing, is essentially inert to the explosive composition and to the materials of construction of the military bomb 10. The present tail pad and seal is cured essentially at room temperature and does not introduce any thermal hazards into the bomb assembly process. The present tail pad and seal has elasticity properties and compressibility properties which are eminently suitable to the requirements of a military bomb. The present tail pad and seal can be cured substantially completely to a thermoset condition in a predeterminable cure time, preferably ranging from about 5 minutes to about 2 hours. Cure time can be adjusted by varying the amount of catalyst and by adjusting the ratio of reactive to non-reactive components of the composition. When employing the present composition, the tail plug 19 may be inserted into the military bomb assembly prior to the complete cure of the tail pad. This capability facilitates the speed of bomb assembly completion. The bombs can be removed from the assembly area and stored vertically or horizontally or otherwise even where the explosive composition 25 has not completely congealed. The tail plug 19, upon insertion, may engage the tail pad and seal and be adhered in the assembly by such engagement.

A typical overall composition, both Component A and Component B includes:

parts by weight polybutadiene resin, hydroxy terminated, having a viscosity of 5,000-6,000 CPS at 86 F; a hydroxyl content of 0.80 meg/gm and an equivalent weight of about 1,250;

5 parts by weight petroleum asphalt, air blown,

having a ring and ball softening point, 155 F;

5 parts by weight of an extender oil which is miscible with the petroleum asphalt;

1 part by weight Mondur-MR, a polymethylene polyphenyl polyisocyanate having a functionality of approximately 4;

0.005 parts by weight dibutyl tin dilaurate, which is a catalyst for the reaction between polyisocyanate and hydroxyl terminated polybutadiene resin.

These ingredients are mixed well and poured as a liquid on top of the explosive composition 25.

INGREDIENTS The hydroxyl terminated polydienes and their preparation are described in Canada Pat. No. 777,223. In general these diene polymers have primary hydroxyl groups and are formed from 1,3-dienes having four to 12 carbon atoms. The initial dienes may be unsubstituted or 2-substituted or 2,3-disubstituted dienes. The hydroxyl functionality is preferably greater than 2, for example, from about 2.1 to about 2.6 although higher functionalities are permissible.

The polyisocyanate is employed as a cross-linking agent for the diene polymers and is a material containing at least two isocyanate radicals. Preferably, the polyisocyanate has a molecular weight greater than about 200 to minimize toxicity hazards. Useful polyisocyanates are 4, 4'-diphenylmethane diisocyanate, 1,5- naphthalene diisocyanate, phenylene diisocyanates, p, p'-diphenylmethane diisocyanate, hexamethylene diisocyanate. Polyarylene polyisocyanates are a preferred material. Isocyanate terminated prepolymers also can be employed as the polyisocyanate, for example, the reaction product of tolylene diisocyanate or other polyisocyanates with dihydric or diamine terminated polyesters, polyethers or polyamides. In general, the ratio of the polyisocyanate material to the hydroxyl terminated polydiene is such that there are about 0.5 to about 5 isocyanate groups per hydroxyl group of the diene polymer, and preferably from about 1.0 to 2.0 isocyanate groups per hydroxyl group of the polydiene ingredient.

THE CATALYST In order to achieve a reaction between the polyisocyanate and the hydroxyl terminated polydiene in a commercially feasible period of time, typical polyurethane catalysts are employed such as dibutyl tin dilaurate, stannous octoate. In general, the amount of catalyst is from about 0.005 to about 0.1 parts by weight based upon parts by weight of the polydiene polymer. The polyisocyanate is normally maintained separate from the catalyst during storage and prior to the mixing of the ingredients of the present tail pad and seal. That is, the catalyst is provided in the same component with the hydroxy terminated polydiene.

PETROLEUM ASPHALT EXTENDER Petroleum asphalts have been used as sealants in military bombs. Their inertness is a useful property in the present tail pad composition. The asphalts for this purpose preferably have a ring and ball softening point of about l50-l80 F in order that the resulting composition will have a suitable hardness. The hardness or tackiness of the petroleum asphalt can be modified by the introduction of suitable plasticizers such as petroleum oils of the type normally used as rubber extender oils. The amount of plasticizer is determined by the desired hardness and tackiness in the resulting composition provided that excessive bleeding of the composition does not develop.

PROPORTIONS The proportions of hydroxyl terminated polydiene resins and the polyisocyanate in the composition have already been discussed. These two ingredients together with the catalyst constitute a polyurethane rubber composition. The rubber composition can be extended with petroleum asphalt with or without plasticizers in an amount ranging from about 0.5 to about 2.0 times the weight of the polyurethane rubber composition.

STORAGE AND MIXING Preferably the present compositions are provided in two packages which can be admixed to produce the desired adhesive composition. The amount and type of catalyst is preferably selected to produce a cure time of 5 minutes to 2 hours. Preferably the polyisocyanate is combined with a portion of the petroleum asphalt in an ingredient mixture identified as Component B. The hydroxyl terminated polydiene resin is mixed with another portion of the petroleum asphalt and the catalyst and is identified as Component A. The mixtures A and B preferably have about equal volume and about equal viscosity to facilitate the mixing. In a preferred combination, the following ingredients are assembled:

Mixture A 2,9[5 grams polybutadiene resin, hydroxy terminated, available from Arco, Inc. under the trade name Poly-BD Resin 45M, a hydroxyl terminated resin fabricated from polybutadiene and having a viscosity of about 5,000 centipoises at 30 C and a hydroxyl content of 0.80 meq/gm 582 grams petroleum asphalt having a ring and ball softening temperature of 159 F 15 grams dibutyl tin dilaurate as catalyst.

Mixture B 300 grams Mondur-MR, a polyisocyanate based upon polyphenylene polymethylene 2,318 grams petroleum asphalt, the same material as provided in Mixture A 1,242 grams Tufflo-300 oil, a petroleum oil for Arco,

Inc. It may be desirable to incorporate some molecular sieves (for example, Linde type 4A powder) in Mixture B prior to incorporating the polyisocyanate in order to tie up any available water and increase the storage life of the resulting Component B.

In order to prepare the present sealant composition, equal volumes of Mixture A and B are combined with a mechanical stirring device for several minutes. Preferably and normally the resulting mixture will flow readily at room temperature. The described composition will set in about minutes as a thermoset cured elastomer. Where the composition is applied on top of a warm explosive charge, the heat will accelerate the cure. The term thermoset" as employed herein is intended to comprehend the three-dimensional character of the polymerization and is not intended to refer to any requirement for heat dependency to achieve curing. One of the virtues of the present tail pad composition is that it can be cured substantially without exotherm, thereby minimizing any possible hazards to the bomb making facility.

What is claimed is:

1. In a military bomb comprisinga body having a closed nose end and an open tail end, a charge of explosive material within the said body terminating adjacent to the said open tail end, a tail pad of sealant communicating with the inner wall of said body and covering the tail portion of said charge, the improvement com- PIlSll'lgI a self-adhering connection between the tail pad and the said charge, and a self-adhering connection between the tail pad and the said inner wall, and as the tail pad, the thermoset reaction product of asphaltic filler; hydroxy terminated polydiene polymer; non-volatile organic polyisocyanate; a catalyst for the reaction of isocyanate groups and hydroxyl groups. 2. The military bomb in claim 1 wherein the said reaction product includes particulate tiller.

3. The military bomb of claim 1 wherein the said asphaltic filler is extended with a mineral plasticizer oil. 4. The military bomb of claim 1 wherein the bomb includes a tail plug for sealing the said open tail end, the said tail plug having a self-adhering connection with the said tail pad. 

2. The military bomb in claim 1 wherein the said reaction product includes particulate filler.
 3. The military bomb of claim 1 wherein the said asphaltic filler is extended with a mineral plasticizer oil.
 4. The military bomb of claim 1 wherein the bomb includes a tail plug for sealing the said open tail end, the said tail plug having a self-adhering connection with the said tail pad. 